The present application relates generally to heat exchangers and more particularly relates to a single pass cross-flow heat exchanger with improved temperature distribution.
Heat exchanging systems, employing heat exchangers, are widely used in applications such as space heating, refrigeration, air conditioning, power plants, chemical processing plants and numerous engines, machines, vehicles and electrical devices. Heat exchangers may be employed in these various applications for efficient heat transfer from one medium to another, and more particularly to exchange heat between two fluids. For example, a first fluid at a higher temperature may be passed through a first channel or passageway, while a second fluid at a lower temperature may be passed through a second channel or passageway. The first and second passageways may be in contact or close proximity, allowing heat from the first fluid to be passed to the second fluid. Thus, the temperature of the first fluid may be decreased and the temperature of the second fluid may be increased.
In general, heat exchangers may be classified according to their flow configuration as crossflow heat exchanging systems, parallel heat exchanging systems, counter flow heat exchanging systems, or in terms of their geometry and design as shell and tube heat exchangers, plate heat exchangers, and finned tube heat exchangers, among many others.
One of the main design goals in the construction of heat exchangers focuses on maximizing heat transfer while minimizing the pressure loss therethrough. Generally described, the extent of the pressure loss and heat transfer factors into the operating costs and the overall energy losses and efficiency of the heat exchanger and its use. Accordingly, in heat exchange applications it is advantageous to utilize a design with a low-pressure loss and a relatively high heat transfer. Of particular concern here are single-pass cross-flow heat exchangers employing multiple tube rows or similar passageways that are commercially available and suitable for use in heat exchange applications where the volume flow rate of a tube-side fluid inside the tubes is too high to pass through a single row of tubes in a crossflow configuration with a fin-side fluid.
Two critical issues emerge when designing a heat exchanger with multiple tube rows in parallel in a single-pass cross-flow arrangement e.g. for a superheater or reheater section in a heat recovery steam generator (HRSG), an air-cooled condenser or for a gas turbine (GT) recuperator. One such issue relates to the tube-side fluid outlet temperatures and the heat duty of the individual tubes as they may differ significantly from the first to the last row. Another issue relates to the temperature distribution over the cross section of the fin-side fluid exiting the heat exchanger being low on one side and high on the other side.
Accordingly, there is a desire for an improved single-pass cross-flow heat exchanger that provides an even fluid temperature distribution of a tube-side fluid exiting a tube-side fluid flow path without uneven heating and hot spots as well as an even fluid temperature distribution of a fin-side fluid exiting a fin-side fluid flow path. The improved design provides for a lower maximum tube temperature, more even tube side outlet temperature distribution, thus enabling lower grade materials and increased lifetime from reduced thermal loads and stresses. Such a heat exchanger preferably may be used for a variety of gas to gas, gas to liquid or gas to steam heat transfer applications and specifically may be used for steam superheaters, steam reheaters, gas turbine recuperators or air-cooled condensers in power plants.